This invention relates to a valve structure having a movable valve member controlling fluid flow through a fluid passage and designed particularly for resistance to high temperatures and being subjected to fire.
With safety becoming of increasing importance, the employment of valves which do not fail or leak when subjected to fire is highly desirable. In pipelines which convey inflammable fluids such as petroleum products, valves must be tightly sealed in a closed position and in the event of fire, the valve member must be tightly sealed even though the valve seals might be destroyed or impaired.
Heretofore, so-called fire-safe valve structures have been provided in which the valve seals in contact with a movable valve member, such as a ball valve member, have deteriorated or been partially consumed by high temperatures and the ball valve then moves into metal-to-metal contact with the adjacent metal seat. The prior art devices depended on the resilient face seal for the movable valve member deteriorating or being destructed by the fire or high temperatures. For example, prior U.S. Pat. No. 3,174,495 dated Mar. 23, 1965 discloses a fire-safe ball valve in which a ball valve structure is provided with a resilient sealing member which disintegrates or is consumed during a fire. In addition, U.S. Pat. No. 3,174,495 discloses a fusible material provided adjacent the trunnions of the ball valve with the fusible material disintegrating at high temperatures to permit movement of the spherical valve member into contact with the metal seat.
U.S. Pat. No. 3,843,091 dated Oct. 22, 1974 shows an arrangement in which a resilient face seal formed of polytetrafluoroethylene has a void space behind it to permit flow of the face seal into the void space upon softening of the face seal by a fire thereby to permit a metal-to-metal contact between the movable valve member and the adjacent metallic seat.